Indoor air quality-related health issues are major occupational and environmental problems. Some of the reported health effects include: dry eyes and throat, rhinitis, lethargy, headache, chest tightness, wheezing and asthma. Work related asthma (WRA) is one of the more severe adverse reported health effects, and can take the form of pulmonary irritation, allergic asthma, or exacerbation of pre-existing asthma. Asthma and other adverse health effects may result from exposures to chemicals, but unfortunately, the hazards associated with the indoor environment are not well-understood or well-characterized. Exposures of mixed chemical classes, such as particulate matter and oxygenated organic species, including; biologically active oxidized volatile organic compounds (VOC), contribute to these symptoms. Consumer cleaning products and air fresheners contain chemicals such as &#945;-terpineol, which can react with ozone to form a variety of secondary pollutants that may contribute to the symptoms described above. These secondary pollutants include oxygenated organic chemicals, such as aldehydes, ketones, carboxylic acids and dicarbonyls. Unfortunately, these volatile reaction products may go undetected by conventional sampling methods and lead to inaccurate exposure assessments of indoor environments. There is limited knowledge regarding exposure to complex mixtures, particularly the secondary products from potential interactions among VOCs and other indoor air pollutants. Studies exposing animals to products of chemical reactions, such as ozone with limonene, have demonstrated that the reaction products have a significant impact on the breathing rate of exposed animals when compared to animals exposed to the reactants separately. A 1-hour exposure of mice to the oxidation products of ozone and limonene resulted in a significant increase in upper airway irritation and airflow limitation compared to exposure to the parent compounds. These findings suggest that the secondary pollutants generated from indoor air chemistry may exacerbate lower airway symptoms or occupational asthma in individuals involved in industrial cleaning operations. The studies conducted as part of this interagency agreement have developed and are working to validate a novel in vitro indoor air exposure system which will help to further characterize the effects of occupationally relevant indoor air compounds on the respiratory tract. This novel system has been used specifically to evaluate secondary pollutants (i.e. ozone + commonly used VOCs) with conserved structures generated through reactive indoor air chemistry, such as dicarbonyls and carboxcylic acids, on the respiratory tract. Research results from this project are anticipated to clarify this potential association and improve worker exposure assessment by more clearly identifying how indoor air constituents, generated from products used in offices and health care settings may result in health effects. In addition, the proposed research results can also potentially be used in interventions such as chemical selection or substitution, building maintenance procedures, and improved exposure assessment which will help to promote safe and healthy workplaces by reducing or eliminating the impacts of WRA and other health effects associated with indoor air exposure. This research will fill an important gap in the understanding and quantification of workplace (offices and healthcare) exposures to secondary pollutants generated from indoor chemistry. This information gained from these studies will provide direction for which chemicals/mixtures should be investigated for additional risk assessment studies. This project specifically meets the NTP goals of: providing toxicological evaluations on substances of public health concern, developing and validating an improved high throughput alternative toxicology method with increased sensitivity and specificity that also allows for reduced animal usage, and provide data that will improve understanding of fundamental health effect mechanisms and help to strengthen the base for future risk assessment for indoor air exposure.